Modified gelatin for photographic purposes and process for rendering compounds for photographic layers resistant to diffusion



United States Patent 3 Claims. 01. 106-135) ABSTRACT OF THE DISCLOSURE The invention relates to a process for modifying photographic gelatin by reacting the gelatin with carboxy-lic acid azides, the acid azide group being the substituent of a photographically active additive which is in this way rendered resistant to difiusion.

Photographic materials often contain chemical compounds which must be present in precisely determined layers of the material.

Thus, for the production of multi-color photographic images it is important that the color-forming substances be incorporated in a diffusion-fast manner in certain layers of the photographic material. It is known that these conditions can be achieved by providing the color-forming substances with bulky molecular groups which prevent diffusion, for example, long-chained alkyl groups. The molecular weights of such color-forming substances often exceed 500 although the actual color-forming part has a molecular weight of scarcely 150. It is further known to prevent diffusion of certain compounds in the photographic material by combining them with macro-molecular substances which are then added to the photographic emulsions. However, the addition of such relatively large molecules of a different type generally impairs the physical properties of the photographic layer which customarily contains gelatin as binding agent, especially the waterpermeability or the ability to swell and the viscosity of the casting solutions. Furthermore, it is known to introduce chemical compounds into photographic gelatin emulsions in such a way that they are fast to diffusion by reacting their acid halides, especially their acid chlorides, directly with photographic gelatins. Since the gelatin always contains free amino and hydroxyl groups, the corresponding compounds are bound to the gelatin chemically as amide or ester type compounds. This reaction, however, is of limited utility since it always involves considerable changes in temperature and fluctuations in pH which cause other changes in the gelatin, in particular uncontrollable degradation reactions, apart from the desired acylation. This largely renders the gelatins useless for photographic material.

It is among the objects of the present invention to provide a process for rendering organic compounds which are photographically active, fast to diffusion by reacting the said compounds with gelatin. Another object is to provide a photographic material containing the compounds produced by the said process. Still other objects will become apparent from the following description.

We now have found that compounds which are to be added to photographic layers can be linked chemically to gelatin and thereby rendered diffusion resistant without impairing the gelatin by reacting the carboxylic acid azides of the said compounds with gelatin.

Compounds which can be used for that reaction are characterized by containing at least one acid azide group of the formula CON 3,404,017. Patented Oct. 1, 1968 The present process for linking organic compounds to gelatin can be applied to all compounds which are photographically active, that is, which are incorporated into a photographic material to influence the photographic properties or the mechanical properties of the material. The function and the chemical structure of the compounds are not critical, the only condition which has to be met is that they contain a CON group capable of reacting with the gelatin in particular the amino or hydroxyl groups of the gelatin so that they are linked to the gelatin through the bivalent CONH- or C0.0-radicals.

Suitable compounds for the reaction of the present invention are, for example, color couplers, optical brightening agents, filter dyes, developers, antifoggants or hardening agents. The method of the invention exhibits particular utility for the reaction of gelatin with color couplers, hardening agents and optical brightening agents.

The following compounds are particularly useful as reaction components with a gelatin.

Color couplers: Color couplers can be-used which yield magenta, cyan or yellow dyes upon reaction with the oxidation products of a color-forming developer, for example, yellow couplers of the fl-keto anilide type, cyan couplers such as phenols or naphthols, or magenta couplers of the pyrazolone type. Suitable couplers are described by P. Glafkides Photographic Chemistry, vol. -2, pages 600-603, published (1960) by Fountain Press, London. As to pyrazolones we refer to the publication of O. Wahl in Angew. Chemie 64 (1952) pages 259-265. Further suitable couplers are indazolones, couplers with cyanacetyl groupings or pyrazolobenzimidazoles such as disclosed in British Patent No. 918,128. Specific color couplers useful as reaction components are:

VI C Hz-C O OH Hardening agents: Suitable hardening agents are, for

where In principle, any desired compound which has an acid group which can be converted into the corresponding azide is suitable. The photographically active part of the molecule may contain several acid azide groups, preferably between 1 and 2 azide groups.

The process of the invention is preferably performed by reacting the photographic reactive compound with gelatin in an aqueous medium. Temperatures of between and 100 C. preferably between and 50 C. are used. The pH of the reaction medium is maintained at about 69 during the reaction.

For example, the azide may be added to a gelatin solution diluted with water, preferably a 10% solution, at slightly elevated temperatures, for example, to and the components left to react for A2 hour, the pH being maintained at the neutral point by the addition of a small amount of alkali. The treated gelatin may be dried and redissolved as desired and, for example, admixed with a photographic silver halide emulsion.

On the other hand, it is also possible to prepare a silver halide emulsion using such a modified gelatin as the protective colloid. Further, it is possible to react the gelatin of a photographic gelatin silver halide emulsion with an azide by the process described above. Similarly, the azide may be added to the gelatin, for example, to one layer, by a bath.

If the molecule of the organic compound carries two or more azide groups, such compounds may be used to harden the gelatines.

The photographic compounds which have been rendered diffusion resistant by chemical linkage to gelatine may be added both to silver halide emulsion layers and to auxiliary or intermediate layers. Thus, for example, the so-called colorless couplers which react with the oxidation product of a color-forming developer to form a colorless compound and which are rendered diffusion resistant by the reaction according to the invention may be added to intermediate layers in photographic rnulti-layered materials used to produce color images, for the purpose of improving color separation.

As silver halides for the light-sensitive emulsions, it is possible to employ silver chloride or silver bromide, possibly with a few mol percent of silver iodide, or mixtures of these halides.

The usual hydrophilic colloids are suitable as binders, such as, advantageously, gelatin, although this can be wholly or partially replaced by other film-forming materials, such as carboxymethyl cellulose, polyvinyl alcohol, alginic acid or derivatives thereof, such as salts, esters or amides, polyvinyl pyrrolidone and the like.

The emulsions stabilized in accordance with the present invention can be chemically sensitized by any of the accepted procedures. The emulsions can be treated with salts of the noble. metals such as ruthenium, rhodium, palladium, iridium and platinum. Suitable compounds are well known in the art. The emulsions can also be sensitized with gold salts as described by R. Koslowsky, Z. wiss. phot. 46, 72 (1951).

The emulsions can also be chemically sensitized with reducing agents such as stannous salts, polyamines, sulfur compounds, such as described in the US. Patent No. 1,574,944, polyethylene oxides and the like. The emulsions can also be optically sensitized with the ordinary sensitizing dyes, cyanines or merocyanines. The emulsions can be stabilized with any of the known stabilizers such as mercury compounds, triazoles, azaindenes, such as disclosed by Birr in Z. wiss. phot. vol. 47 (1952) pages 2-28.

The emulsions may behardened by any suitable hardener such as formaldehyde, halogen substituted aliphatic acids such as mucobromic acid.

The acid azides required for carrying out the process can be prepared by known methods. Suitable methods are described by Houben-Weyl, Methoden der organischen Chemie, vol. VIII, part III, pages 680-684 published by Georg Thieme Verlag, Stuttgart 1952. For example, sodium azide may be caused to react with an acid chloride or an acid hydrazide may be reacted with nitrous acid. The quantity of azide reacting with gelatin is limited by the number of free amine or hydroxyl groups in the gelatin. As a rule, not all these groups enter into the reaction. Moreover, the quantity of azide is responsible for a certain increase in viscosity of the gelatin, which depends also on the type of azide used. The desired properties can easily be obtained by varying the concentration of the azide. Preferably the gelatin and the photographically active compound containing the N cO -group are reacted in a ratio by weight of 1:0.1 to 1:02. The molecular radicals linked to gelatin in this way can no longer be removed even by washing the gelatin for many days. The mode of action of the process according to the invention is demonstrated by the following examples.

Example 1 10 g. of gelatin are caused to swell in ml. of water at 45 C., 1.5 g. of compound III is added to this with stirring, the mixture is stirred for another 30 minutes and during this time the pH is constantly kept adjusted to 8 to 9 with 1 N sodium hydroxide solution. The viscous solution is suction-filtered and can then be shredded and dried. 6 g. of the dry product is dissolved in 50 ml. of water at 45 C. Alternatively, if desired, the reaction mixture may be halved directly after the reaction of gelatin with compound III, which corresponds to about the same amount.

The solutions prepared by these various methods are stirred with ml. of a silver halide gelatin emulsion and the mixture is cast onto a support, e.g., of a transparent polymer, for instance, of a cellulose ester such as cellulose acetate, a polyester such as polyethylenterephthalate, or a polycarbonate particularly of bisphenyl alkanes, or a paper support.

The photographic material prepared by this process is exposed in the usual way after drying, developed with a color-forming developer of the p-phenylenediamine type, e.g., p-diethylamino-aniline, and then bleached and fixed in the usual way.

A diffusion resistant magenta dye image is obtained.

Example 2 2 g. of compound VI, which can be prepared from the corresponding coumarin by reaction with hydrazine followed by reaction with nitrite, are stirred at 45 C. into a solution of 10 g. of gelatin and 90 ml. of waer. During the next 30 minutes, the pH is constantly adjusted to between 8 and 9 with 1 N sodium hydroxide solution. The solution is suction-filtered, left to solidify and the product is shredded. The strongly fluorescent gelatin can then be washed for two days under running water. The fluorescence is maintained. Gelatines prepared in this way can be used as optical bn'ghteners in photographic material.

Example 3 g. of gelatin are swelled in 90 ml. of water, and 1.5 g. cf compound II and a small amount of 1 N sodium hydroxide solution are added, with stirring, at 45 C. so that the pH is maintained at 8 for 30 minutes. The solution is then suction-filtered, left to solidify and then shredded and dried. 6 g. of the dry substance are dissolved in 50 ml. of water at 45. This corresponds to about half the solution obtained before solidification, but if desired this solution may be stirred immediately into 150 ml. of silver halide gelatin emulsion without first drying it. The photographic emulsion prepared by one of the two methods is applied in the usual way onto a support and dried. After exposure, chromogenic development, bleaching and fixing, a cyan, diffusion resistant dye image is obtained.

We claim:

1. In the process of incorporating a photographic additive of the class consisting of color couplers, optical brightening agents, dyes, developers and antifoggants in a gelatin emulsion layer, the improvement according to which the additive is provided with at least one 0 N 0: group 0 N C= group 3. The combination of claim 1 in which the additive is an optical brightening agent and it is provided with only one o N C group References Cited UNITED STATES PATENTS 2,282,001 5/1942 Russell et al. 96-100 X 2,881,046 4/1959 Rose et al. 8127.6 3,143,423 8/1964 Reynolds et al. 9691 NORMAN G. TORCHIN, Primary Examiner.

R. E. MARTIN, Assistant Examiner. 

